97 98 99 Bonneville headlight switch

I've had this car for 6 or 7 years now and I have never been convinced the headlight switch is working properly. It has the Twilight Sentinel feaure. The problem was, the headlights stayed full on low beam at all times. As soon as you'd turn the ignition key on, the headlights would come on. Every great once in a while, the dash lights would dim and come on bright again. Working the headlight switch plunger itself had no effect on what the headlights would do. For the longest time, I figured the headlight switch was bad.

I finally decided to read the owner's manual (imagine that) to see what it had to say about the headlights. It was only after I did read that information that I had an idea about how the headlights were supposed to work.

All of these cars have the Daytime Running Light (DRL) feature, whereby the headlights come on about half bright on low beams as soon as you put the car in gear. When the light outside gets below a certain level, a sensor on the instrument panel turns the headlights on full bright low beam. If you are in a full-light situation where the sensor has the headlights in the DRL mode, you may turn them on full power low beam using the plunger in the switch. If you are parked and the headlights are off, you may use the plunger to turn the lights on and off; otherwise the plunger isn't used much.

I never use the Twilight Sentinel feature (switch under plunger knob that if turned on, will leave your lights on for a certain period of time after you shut the car off to give you time to get into the house using that light).

So, my headlights weren't doing what they were supposed to. It occurred to me to do something simple. Clean the dust out of the little dark blue eye on the light sensor on the left upper side of dash. My wife uses this car and it's always clean inside, but nobody has ever thought to dust the sensor. I just ran a Q-tip around in the little eye a few swipes. The next day, the headlights were working just like the owner's manual said they should. No lights on with car running and in park; come on half strength (DRL) when put in gear; and come on full strength in shade or darkness. Instrument lights come on bright with DRL on; dim when headlights are full on.

Somewhere along in there, I went to the junk yard and taught myself how to change a headlight switch on a 99 Bonneville SLE which is just like my 97 SSEi with respect to the lights. This was a "just in case" so I have a spare switch now if I ever need it (but probably won't).

In case you ever need to know, the headlight switch comes out straight toward you in the driver's seat; it's impossible to do it from under the dash like an old Ford. You have to remove the dash knob (little ring under the plastic that pushes in to release), pull the Twilight Sentinel switch straight off, take off the plastic trim above the instrument plexiglas (three screws), unplug the cigar lighter, and three Torx screws hold the h/l switch in. It's a very tight fit getting it out, but once you do that, carefully unplug the wiring pigtail and Bob's your uncle.

Comments

I have a 95 bonneville and periodically the taillights will go out...it happens sometimes at night which really worries me. There are also times where I will apply the brakes and the instrument panel lights will come on. anybody have any diagnosis for this?

I have a 1998 Pontiac Bonneville, recently its as if a ghost took over the interior lighting and the locks. the lights won't go out until the 10 minute timer is up (when the car is off and locked) Also, the locks no longer unlock when you shift into park. Sometimes they will lock by themselves and the interior lights will come on again and won't go off no matter how far you drive. I used to be able to get them to turn off by cycling the lock switch in the car but not anymore. Any help would be greatly appreciated.

You probably should look into buying a factory service manual for your Bonneville that is from Helminc.com. These are the ones you got if you ordered from the back page of the glovebox manual. They are on Ebay sometimes: the originals from Helminc.com are around $135 if I recall.

You may have a problem with ground at the battery terminal. Check for corrosion. Then check the positive cables. They overlap and are jointly bolted to the positive. People talk about cutting back into the plastic of each to look for deterioration. Also check the spacer between them for corrosion.

Be sure to turn to heater controls OFF while the car is running before disconnecting battery espeicially if you have auto control heater/AC.

You may have a ground buss problem at the ground connection just where the driver's foot goes over the door sill. They corrode and cause funny things to happen.

Also a problem with a weak battery may cause strange symptoms, but yours don't sound like what people often describe.